Featured Article Summary #256

Misti is an active volcano in the southern Peruvian Andes, rising above Arequipa, Peru’s second-largest city. It has a steep shape with two summit craters, and the inner crater contains an active lava dome with vents that release volcanic gases. The summit is 5,822 meters above sea level and is often snow-covered, though there are no glaciers. The volcano formed in four main building stages involving lava and domes, followed by collapses that created crater-like depressions, and over the last 50,000 years it has had many strong explosive eruptions. Today, Misti is considered extremely dangerous because it is only about 12 km from a city with over one million people, and future eruptions or gas emissions could affect neighborhoods, key infrastructure, and cause fast-moving volcanic mudflows. Monitoring and public hazard mapping improved after 2005 when an observatory and awareness efforts were set up, and in the past the Inca made sacrifices there during a major eruption. The name “Misti” may come from Quechuan or Spanish and is linked to ideas like “mixed” or the volcano’s snow cover. Indigenous names include Putina (“mountain that growls”) and Aymara terms like Anukara (“dog”), all referring to how the volcano looks from the Altiplano; “Misti” became common from the 1780s, and other older Spanish and local names also exist. People have lived in the region for more than 1,500 years, and by the Spanish arrival it was already densely settled with roads, canals, and buildings; the city of Arequipa was founded in 1540, and Misti is considered the city’s “house mountain.” Misti is Peru’s best-known volcano, rising just north of Arequipa and visible from the Pacific Ocean. Its surrounding area includes old Inca routes and is now part of Peru’s Arequipa Department, with roads along the volcano’s different sides and dams and hydroelectric plants on the Rio Chili that supply power to Arequipa. Long ago, people built structures on Misti’s crater and possibly had Inca ceremonial uses, though these were later destroyed. In 1893 Harvard installed a high-altitude weather station on Misti, and research there (and at a second base station) helped study the atmosphere and how humans respond to high elevations; these stations closed in 1901, and later storms erased most traces, though some scientific observations continued during the 20th century. Peru’s volcanoes belong to the Central Volcanic Zone of the Andes, which stretches about 1,000 km from southern Peru through Bolivia to northern Argentina and Chile. Many of these volcanoes are not well studied because the region is sparsely populated, though several were active soon after the Spanish conquest and others are still found across Peru. Ubinas is the country’s most active volcano, and major eruptions like Huaynaputina in 1600 caused large loss of life, while more recent eruptions of Sabancaya and Ubinas severely affected local communities. Misti is a young, steep, symmetrical stratovolcano about 20 km wide, rising roughly 3.5 km above Arequipa. Its summit has two nested craters: a large outer crater and a smaller inner one with very steep walls made of volcanic debris, plus an internal dome with cracks, boulders, sulphur deposits, and active fumaroles. From the summit, other Western Cordillera peaks such as Ubinas and Pichu Pichu can be seen, and the highest point on the northwestern rim is marked by an iron cross. The cone is built from pyroclastic rocks and short lava flows, with a thick layer about 2.2 km deep, and it sits on older, more eroded volcanic material beneath it. Surrounding areas include a wide fan of volcanic debris and ash fields formed by wind, and the south side has deep ravines while the north is flatter. Misti also shows signs consistent with a sector collapse: a narrow chute on the northwestern flank and large debris-avalanche deposits to the southeast and southwest, covering tens to about 100 km².